Alveolar macrophages play a key role in lung homeostasis and macrophage lipid metabolism, concomitant with synthesis of its lipid mediators, significantly influences normal and pathophysiologic lung function. Therefore, our investigations of macrophage lipid metabolism are vital to understanding lung homeostasis and the variety of lung dysfunctions. Bis(monoacylglycerol)phosphate (BMP) comprises 18% of the phospholipids in alveolar macrophages. This phospholipid is unique in eukaryotic tissue with its sn-glycero-1-phosphoryl-sn-1'-glycerol stereoconfiguration that contrasts with the usual sn-glycero-3-phosphoryl-sn- 1'-glycerol isomer found in all other phospholipids. Evidence exists, however, that the sn-glycero-3-phosphoryl- sn-1'glycerol is synthesized also but does not accumulate in macrophages. BMP is derived from exogenous phosphatidylglycerol from lung surfactant and contains high levels of unsaturated fatty acids including arachidonic acid that can be involved in eicosanoid synthesis. For these reasons we propose to study: 1) The mechanism(s) by which both BMP isomers is synthesized 2) How the fatty acids are turned ever in BMP 3) What accounts for the stability of the sn-glycero-1- phosphate isomer of BMP in cells 4) Where the precursor phosphatidylglycerol is localized in the macrophage 50 Where the enzymes of BMP metabolism are localized in the cell Many of the proposed studies will employ the model macrophage cell line RAW 264.7. All key observations will be verified using human alveolar macrophages so that we can determine the route of BMP metabolism in human lung. Considerable emphasis will be placed on determining the relative contribution to two pathways for BMP synthesis that lead to the formation of different stereoisomers. Since only one isomer (sn-glycero-1-phosphoryl-sn-1'- glycerol) accumulates, we believe that phospholipases in the macrophages selectively degrade the other (sn-glycero- 3-phosphoryl-sn-3-glycerol) isomer formed. We also will test the hypothesis that the endosomal pathway is involved in phosphatidyl-glycerol uptake and conversion to BMP. These studies, therefore, should establish the mechanisms of BMP metabolism including the route of entry of the precursor molecule into the cell. We also will determine how the acyl groups are turned over emphasizing the significance of arachidonate removal that may relate to eicosanoid synthesis.